1. Field of the Invention
This invention relates to an improvement in a resinous die for pressing a blank material into a desired shape.
2. Description of the Prior Art
A vehicle body panel for forming a vehicle body is provided by pressing a blank material in a pressing die into a desired shape. Known pressing dies are made from cast iron or steel. Pressing dies made from cast iron or steel have excellent durability. Thus, the relatively high costs of such pressing dies can be recovered by mass producing intended products.
In recent years, however, automobiles are subjected to frequent model changes to meet a diversity of demands and are now becoming the targets of diversified-model little production. When pressing dies made of cast iron or steel are used in the diversified-model little production, failure may be experienced in recovering the whole costs of those dies, thus making it difficult to keep the costs of production of intended automobiles to a minimum.
Thus, pressing dies for use in the diversified-model little production are usually made of thermoplastic resins. Such resinous dies greatly contribute to the reduction of die costs compared to the cast iron or steel dies. Thus, use of such resinous dies enables automobile model changes in relatively short cycles without increasing the costs of production of automobiles.
However, such resinous dies can more easily wear out than the cast iron or steel dies because they are less rigid than the latter dies. With forming or shaping portions of the resinous dies worn out, it is quite difficult to ensure precision in the resulting press-shaped articles. To ensure precision in the shaped articles, it is necessary for the dies to be changed before the shaping portions of the dies wear out.
Since the resinous dies need to be changed relatively frequently in order to ensure precision in the shaped article, it is often difficult to fully recover the costs of the dies. Accordingly, there is a demand for a resinous die with increased durability.
It is therefore an object of the present invention to provide a resinous die which has increased durability and hence can keep the die costs to a minimum.
According to an aspect of the present invention, there is provided a resinous die for press-shaping a blank material into a desired configuration, which comprises: a die member including a shaping portion, the shaping portion being formed of an epoxy resin layer provided at portions thereof where a relatively low surface pressure is applied, and a plurality of reinforcing pieces provided at portions thereof where a relatively high surface pressure is applied, for reinforcing the shaping portion; and a punch including a shaping portion, the shaping portion being formed of an epoxy resin layer provided at portions thereof where a relatively low surface pressure is applied, and a plurality of reinforcing pieces provided at portions thereof where a relatively high surface pressure is applied, for reinforcing the shaping portion of the punch.
Those portions of each shaping portion which are applied with a relatively low surface pressure are thus formed of an epoxy resin which is inexpensive compared to cast iron. As a result, the cost of manufacture of the shaping portions and hence the die can be reduced. Further, by virtue of the reinforcing pieces of aluminum-copper-based zinc alloy which have a hardness far greater than that of an epoxy resin and are provided at those portions of the shaping portions where a relatively high surface pressure is applied, the shaping portions and hence the die are imparted with increased wear resistivity, thereby prolonging the life of the die.
It is desired that the reinforcing pieces of the die member and punch have a hardness of about HV 96 kgf/mm2.
Preferably, the reinforcing members of the die member and punch are made of an aluminum-copper-based zinc alloy.
Desirably, the epoxy resin layers of the shaping portions of the die member and punch have a thickness falling in a range of 20-30 mm. The reinforcing pieces of the shaping portions of the die member and punch may be partly embedded in the epoxy resin layers.
Preferably, the die member has a backup portion provided on a reverse side of the shaping portion of the die member for backing up the die member shaping portion. Preferably, the punch has a backup portion provided on a reverse side of the shaping portion of the punch for backing up the punch shaping portion.
In a preferred form, the backup portion of the die member comprises a filler layer provided by hardening a filler formed of an adhesive containing sand. The filler layer preferably has embedded therein frameworks for reinforcing the filler layer, and cooling pipes for passing cooling water therethrough to cool the die member.
In a preferred form, the backup portion of the punch comprises a filler layer provided by hardening a filler formed of an adhesive containing sand. Preferably, the filler layer has embedded therein a framework for reinforcing said filler layer, and cooling pipes for passing cooling water therethrough to cool the punch.
Desirably, the die further comprises a blank holder disposed vertically movably around the punch for holding a flange of the blank material in cooperation with a mating portion of the shaping portion of the die member upon press-shaping of the blank material to thereby prevent wrinkling of the flange of the blank material. The blank holder may comprise an epoxy resin layer provided on a side thereof opposed to the mating portion of the shaping portion of the die member.
In a preferred form, the blank holder comprises a backup portion provided on a reverse side of the epoxy resin layer for backing up the epoxy resin layer. The backup portion desirably comprises a filler layer provided by hardening a filler formed of an adhesive containing sand and having embedded therein cooling pipes for passing cooling water therethrough to cool the blank holder.